The renal, neural, hormonal, and metabolic mechanisms involved in the elevation of arterial blood pressure observed in the squirrel monkey during operant conditioning procedures at high and low environmental temperatures will be studied using behavioral, physiological, pharmacological, and surgical techniques. Studies will be performed in unanesthetized subjects before and after training under operant conditioning procedures, during administrations of norepinephrine and angiotensin, during exposure to hypoxia and hypercapnia, before and after adrenalectomy, before and after surgical denervation of sinoaortic baroreceptors, and at high and low ambient temperatures. Arterial blood pressure, heart rate, cardiac output, and the distribution of cardiac output will be studied by means of catheters chronically implanted in the abdominal aorta, right atrium, and left ventricle. Renal function will be studied using standard clearance techniques in subjects seated in a metabolism chair. Hormonal responses (renin, angiotensin II, and aldosterone) will be studied using arterial blood samples and immunoassay techniques. Metabolic and respiratory responses will be studied by measuring oxygen uptake, carbon dioxide release, pulmonary and systemic arterial pO2, pCO2, and pH, and body temperature. The objective of these studies is to determine the relations between autonomic, hormonal, and skeletal muscle responses to operant conditioning procedures.